This application claims the priority of German Patent Application No. 197 27 588.5, filed on Jun. 28, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process and a system for generating a high-hydrogen, low-carbon monoxide gas.
A system for generating hydrogen by means of partial oxidation and/or the water vapor reforming of methanol is known from German Patent Document DE 44 23 587 C2. In addition to containing hydrogen, the reforming product gas flow also contains carbon monoxide which is undesirable for certain applications, for example, during the conversion of the generated hydrogen in a fuel cell.
For eliminating or at least reducing the carbon monoxide fraction in the high-hydrogen gas, it is also known to connect a gas purification stage behind the gas generating device. Such a gas purification stage is known, for example, from German Patent Document DE 195 44 895 C1, in which the carbon monoxide contained in the high-hydrogen gas is selectively oxidized with the addition of oxygen on an oxidation catalyst.
During starting, the gas generating system must be brought to the operating temperature. This can take place, for example, by heating from the outside or by introducing hot gases. From Japanese Patent Document JP 58-108291 A, it is known, for example, to provide a ceramic core with an electric heating device in a reformer. For generating hot gases, for example, a catalytic combustion on a Pt-containing catalyst can be used. From Japanese Patent Document JP 08119602 A, a gas generating system is known, for example, which has a separate catalytic burner. A hot gas is generated there whose energy is transmitted in an evaporator to the gas to be reformed and thus, during the flow through the reformer, is also transmitted to the reformer. A disadvantage of these systems is the fact that additional components are required for the heating, particularly in the starting phase.
It is an object of the present invention to provide a process and apparatus for generating a high-hydrogen, low-carbon monoxide gas with improved cold-starting characteristics.
This problem is solved by a process and a system according to the present invention.
During the normal operation of a gas generating system, the gas flows through a gas purification stage only after it has flowed through the gas generating device. If a system for the selective CO-oxidation is used as the gas purification stage, which generally contains a platinum-containing catalyst for removing the carbon monoxide from the high-hydrogen gas, the system can temporarily be operated as a catalytic burner during the starting phase in a simple manner by a reversal of the flow direction so that the gas generating system can easily and rapidly be brought to the necessary operating temperature. Additional components, apart from corresponding switching valves, are not required for this purpose. Thus, a compact system is created.
If this flow reversal principle is used in a gas generating device in which, in addition to or instead of the water vapor reforming, partial oxidation is also carried out, another advantage results. A platinum-containing zone which in the normal operation is disposed in front of the reforming area would necessarily lead to a two-stage method of operation. In the normal operation, the oxygen in the gas flow would be completely consumed in the platinum-containing zone, which is highly active for the combustion. As a result, large amounts of heat are released in the platinum-containing zone which must be transported into the reforming area. Should this two-stage operating method not be desired, the flow through the platinum-containing zone is permitted only during the starting phase, which would result in an exclusive use of this component for the starting phase.
In contrast, by means of the system and process according to the present invention, a simple solution is obtained without a separate reactor or reactor area which is used only during the starting phase.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.